我需要扭转我的NSArray
。
举个例子:
[1,2,3,4,5]
必须成为: [5,4,3,2,1]
实现这一目标的最佳方法是什么?
#1楼
试试这个:
for (int i = 0; i < [arr count]; i++)
{
NSString *str1 = [arr objectAtIndex:[arr count]-1];
[arr insertObject:str1 atIndex:i];
[arr removeObjectAtIndex:[arr count]-1];
}
#2楼
至于我,您是否考虑过首先如何填充阵列? 我正在将MANY对象添加到数组中,并决定在开头插入每个对象,将任何现有对象向上推一个。 在这种情况下,需要一个可变数组。
NSMutableArray *myMutableArray = [[NSMutableArray alloc] initWithCapacity:1];
[myMutableArray insertObject:aNewObject atIndex:0];
#3楼
如果你想做的只是反向迭代,试试这个:
// iterate backwards
nextIndex = (currentIndex == 0) ? [myArray count] - 1 : (currentIndex - 1) % [myArray count];
您可以执行[myArrayCount]一次并将其保存到本地变量(我认为它很昂贵),但我也猜测编译器几乎会对上面编写的代码做同样的事情。
#4楼
NSMutableArray *objMyObject = [NSMutableArray arrayWithArray:[self reverseArray:objArrayToBeReversed]];
// Function reverseArray
-(NSArray *) reverseArray : (NSArray *) myArray {
return [[myArray reverseObjectEnumerator] allObjects];
}
#5楼
一些基准
1. reverseObjectEnumerator allObjects
这是最快的方法:
NSArray *anArray = @[@"aa", @"ab", @"ac", @"ad", @"ae", @"af", @"ag",
@"ah", @"ai", @"aj", @"ak", @"al", @"am", @"an", @"ao", @"ap", @"aq", @"ar", @"as", @"at",
@"au", @"av", @"aw", @"ax", @"ay", @"az", @"ba", @"bb", @"bc", @"bd", @"bf", @"bg", @"bh",
@"bi", @"bj", @"bk", @"bl", @"bm", @"bn", @"bo", @"bp", @"bq", @"br", @"bs", @"bt", @"bu",
@"bv", @"bw", @"bx", @"by", @"bz", @"ca", @"cb", @"cc", @"cd", @"ce", @"cf", @"cg", @"ch",
@"ci", @"cj", @"ck", @"cl", @"cm", @"cn", @"co", @"cp", @"cq", @"cr", @"cs", @"ct", @"cu",
@"cv", @"cw", @"cx", @"cy", @"cz"];
NSDate *methodStart = [NSDate date];
NSArray *reversed = [[anArray reverseObjectEnumerator] allObjects];
NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);
结果: executionTime = 0.000026
2.迭代reverseObjectEnumerator
这速度在1.5x到2.5x之间:
NSDate *methodStart = [NSDate date];
NSMutableArray *array = [NSMutableArray arrayWithCapacity:[anArray count]];
NSEnumerator *enumerator = [anArray reverseObjectEnumerator];
for (id element in enumerator) {
[array addObject:element];
}
NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);
结果: executionTime = 0.000071
3. sortedArrayUsingComparator
速度在30x到40x之间(这里没有惊喜):
NSDate *methodStart = [NSDate date];
NSArray *reversed = [anArray sortedArrayUsingComparator: ^(id obj1, id obj2) {
return [anArray indexOfObject:obj1] < [anArray indexOfObject:obj2] ? NSOrderedDescending : NSOrderedAscending;
}];
NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);
结果: executionTime = 0.001100
所以[[anArray reverseObjectEnumerator] allObjects]
在速度和轻松方面是明显的赢家。
来源:oschina
链接:https://my.oschina.net/u/3797416/blog/3182996